The use of scattered light methods for measuring the concentration of particles in gases and other colloids in dispersion media is known from the related art.
German Published Patent Appln. No. 10 2010 002 423 describes such a scatterometer in which a light-intensive light source directs a light beam into a measuring chamber in which the gas or colloid to be measured is located. Assigned to the measuring chamber are two light sensors which detect the light which is scattered on the particles present in the gas. To check the proper function of such a scatterometer or to calibrate it, it is necessary to set a defined condition in the measuring chamber, at which the light beam of the light source emits a scattered light having a defined intensity and distribution.
For that purpose, it is known from German Published Patent Appln. No. 10 2010 002 423 to provide a calibration device, in which a scattering body is used in the measuring chamber, which emits a scattered light having a defined intensity and distribution when irradiated with the light of the light source, the scattered light being detected by the two light sensors. The calibration device should be able to simulate different concentrations of particles in the exhaust gas. It is necessary to simulate exhaust gas values having different particle concentrations using the calibration device. The scattering body is made of a transparent carrier material having defined scattered light properties. In addition, a tinted layer or a gray glass filter for damping the scattered radiation or damping the light output is provided on the exit side of the scattered light in the direction of the light sensors and/or at the entrance side of the light beam into the scattering body.
If the laser beam used as the light source in the above-described calibration device strikes the scattering body, approximately 3% of the light is diffusely scattered in each case on the entrance side and the exit side. This diffusely scattered radiation is visible as a luminous spot (speckle pattern) on the scattering body. The luminous spot is superposed as interference with the scattered radiation produced on the scattering centers in the scattering body, so that the light sensors reach saturation, because the amount of light that falls on them is too great.